Patents which are typical of the prior art for mechanically or electromechanically controlling refrigeration compressor capacity include the following U.S. Pat. Nos.: 3,885,938; 3,828,152; 3,719,057; 3,581,519; 3,580,006; 3,552,137; and 3,377,816. Increased efficiencies could be realized if each cooling stage could be controlled at a single highest "cut-in" and "cut-out" pressure levels that would insure adequate temperatures in the refrigerated space serve by the evaporator coils.